The present invention relates to apparatus for preventing the erroneous activation of a device and more particularly, to fail safe systems for inhibiting activation of a respirator upon the production of undesired or erroneous patient initiated trigger signals.
In order to assist the breathing efforts of a patient, respirator devices have been commonly utilized. Generally, respirator devices are adapted to operate on a two-phase cycle simulating the inspirative and expirative periods of the respirative cycle of a patient. Respirators may, for example, operate only during an inspirative period to provide a supply of air, or oxgen enriched air, to a patient, thereby reducing the expenditure of energy by a patient necessary to inhale an adequate amount of air. The respirator may be rendered inoperative during the expirative phase of a patient respirative cycle or, the respirator may be adapted to respond to the inhalative efforts of a patient occurring during the latter portion of a normal expirative phase. Thus, rapid breathing by a patient may be accommodated by activating a respirator in response to an inhalative effort of a patient occurring somewhat earlier than the controller programmed time for activation of the respirator in an inspirative phase.
Although respirator devices have been beneficial in assisting the respirative efforts of a patient, it is necessary to assure that such devices do not assume an inspirative phase of operation at a point in time abnormally early in an expirative phase, nor assume a continuous or free running condition whereby air is erroneously supplied after an almost instantaneous expirative phase. Accordingly, it is necessary to provide a fail safe capability with such respirator devices to avoid the foregoing undesirable effects which can result from undesired operation of a respirator device. As previously mentioned, a respirator device may be adapted to be operated in response to the inhalative effort of a patient during the expirative phase of a respirative cycle. Commonly, a patient trigger device is utilized to activate a respirator and a description of an exemplary patient trigger device suitable for use with the present invention is found in U.S. Pat. No. 3,896,800, which is assigned to the assignee of the present invention. Generally, such patient trigger devices include a transducing element for generating an appropriate electrical signal in response to the inhalative effort of a patient. The aforementioned transducer may take the form of a vacuum chamber having a flexible diaphragm forming one surface portion thereof with the chamber placed in communication with a patient by a suitable flexible hose or conduit. An opaque member such as a shutter is preferably mounted on the diaphragm such that in the absence of a vacuum created by a patient inhalative attempt, light generated from a suitable light source is precluded by the shutter from impinging on a light detecting device such as a light dependent resistor. However, upon commencement of an inhalative attempt by a patient, the diaphragm is translated and the shutter member is withdrawn from the light path between the source and light detecting device such that an appropriate electrical trigger signal is thereby generated by the detecting device. The aforedescribed light source, shutter and detecting device or any trigger device that produces an electrical conductivity signal where inspiratory effort is sensed may be utilized with the patient trigger apparatus described in the above-identified co-pending application and may be utilized in connection with the present invention as will be described in greater detail hereinafter.